As the technical problem when using an amorphous alloy ribbon as the material for the iron core of a power transformer, high frequency transformer, etc., the fact that the amount of use of materials at the time of production of the transformer, for example, the iron core and copper wire, becomes greater and the production cost becomes higher than the case of use of silicon steel sheet can be mentioned. This is because most amorphous alloy ribbons have a small saturation magnetization force and reduce the design magnetic flux density at the transformer and, as a result, the cross-sectional area of the iron core becomes larger.
This amorphous alloy ribbon is most generally produced by the single roll method of ejecting a molten alloy onto the surface of a rotating cooling roll from a rectangular orifice for rapid cooling and solidification. The important things in the method of production of an amorphous alloy ribbon by the single roll method are the uniformity of the sheet thickness and surface properties. The quality of the surface properties governs not only the magnetic characteristics of the amorphous alloy ribbon when used as a single sheet, but also the characteristics of the core in the case of use of amorphous ribbons stacked together such as with the core of a power transformer etc. When the surface properties deteriorate, the drop in the lamination factor causes enlargement of the core, the deterioration of the magnetic characteristics causes an increase in the Watt loss and noise, etc. Therefore, various proposals have been made regarding the surface properties of said amorphous alloy ribbon.
For example, in Japanese Patent Publication (A) No. 6-7902, an amorphous metal ribbon having a surface roughness of the roll non-contact surface of an Rz of 1.5 μm or less is proposed, while in Japanese Patent Publication (A) No. 2000-328206, a soft magnetic alloy ribbon with a width of air pockets at the roll surface of 35 μm or less, a length of 150 μm or less, an average roughness of an Ra of 0.5 μm or less, and improved soft magnetic characteristics is proposed. Furthermore, in Japanese Patent Publication (A) No. 2000-54089, an Fe-based amorphous alloy comprising an Fe—Si—B-based amorphous alloy ribbon reduced in area ratio of the air pockets on the surface of the roll surface side to 20% or less to improve the Watt loss characteristics is proposed, in Japanese Patent Publication (A) No. 9-143640, an Fe—Si—B—C-based wide amorphous alloy ribbon for power transformer iron core use cast in an atmosphere including CO2 gas in 40 vol % or more and having a centerline average roughness Ra of the contact surface with the roll of 0.7 μm or less is proposed, and in Japanese Patent Publication (A) No. 9-268354, a low B amorphous alloy superior in magnetic characteristics made of a low B content Fe—Si—B-based amorphous alloy and having a sheet thickness of 15 to 25 μm and a surface roughness Ra of 0.8 μm or less is proposed.
However, the arts proposed in these patent documents were developed taking note of, as a guideline for improvement of the magnetic characteristics, the surface roughness or shape of air pockets of the amorphous alloy ribbon, that is, local physical characteristics of the amorphous alloy ribbon, and were not developed from the viewpoint of the slip property of the ribbon surface governing the magnetic characteristics, lamination factor, workability, etc. when used stacked as in a core of a power transformer etc.